librosa.feature.stack_memory

librosa.feature.stack_memory(data, n_steps=2, delay=1, **kwargs)

Short-term history embedding: vertically concatenate a data vector or matrix with delayed copies of itself.

Each column data[:, i] is mapped to:

data[:, i] ->  [data[:, i],
                data[:, i - delay],
                ...
                data[:, i - (n_steps-1)*delay]]

For columns i < (n_steps - 1) * delay , the data will be padded. By default, the data is padded with zeros, but this behavior can be overridden by supplying additional keyword arguments which are passed to np.pad().

Parameters:

data : np.ndarray [shape=(t,) or (d, t)]

Input data matrix. If data is a vector (data.ndim == 1), it will be interpreted as a row matrix and reshaped to (1, t).

n_steps : int > 0 [scalar]

embedding dimension, the number of steps back in time to stack

delay : int != 0 [scalar]

the number of columns to step.

Positive values embed from the past (previous columns).

Negative values embed from the future (subsequent columns).

kwargs : additional keyword arguments

Additional arguments to pass to np.pad.

Returns:

data_history : np.ndarray [shape=(m * d, t)]

data augmented with lagged copies of itself, where m == n_steps - 1.

Notes

This function caches at level 40.

Examples

Keep two steps (current and previous)

>>> data = np.arange(-3, 3)
>>> librosa.feature.stack_memory(data)
array([[-3, -2, -1,  0,  1,  2],
       [ 0, -3, -2, -1,  0,  1]])

Or three steps

>>> librosa.feature.stack_memory(data, n_steps=3)
array([[-3, -2, -1,  0,  1,  2],
       [ 0, -3, -2, -1,  0,  1],
       [ 0,  0, -3, -2, -1,  0]])

Use reflection padding instead of zero-padding

>>> librosa.feature.stack_memory(data, n_steps=3, mode='reflect')
array([[-3, -2, -1,  0,  1,  2],
       [-2, -3, -2, -1,  0,  1],
       [-1, -2, -3, -2, -1,  0]])

Or pad with edge-values, and delay by 2

>>> librosa.feature.stack_memory(data, n_steps=3, delay=2, mode='edge')
array([[-3, -2, -1,  0,  1,  2],
       [-3, -3, -3, -2, -1,  0],
       [-3, -3, -3, -3, -3, -2]])

Stack time-lagged beat-synchronous chroma edge padding

>>> y, sr = librosa.load(librosa.util.example_audio_file())
>>> chroma = librosa.feature.chroma_stft(y=y, sr=sr)
>>> tempo, beats = librosa.beat.beat_track(y=y, sr=sr, hop_length=512)
>>> beats = librosa.util.fix_frames(beats, x_min=0, x_max=chroma.shape[1])
>>> chroma_sync = librosa.util.sync(chroma, beats)
>>> chroma_lag = librosa.feature.stack_memory(chroma_sync, n_steps=3,
...                                           mode='edge')

Plot the result

>>> import matplotlib.pyplot as plt
>>> beat_times = librosa.frames_to_time(beats, sr=sr, hop_length=512)
>>> librosa.display.specshow(chroma_lag, y_axis='chroma', x_axis='time',
...                          x_coords=beat_times)
>>> plt.yticks([0, 12, 24], ['Lag=0', 'Lag=1', 'Lag=2'])
>>> plt.title('Time-lagged chroma')
>>> plt.colorbar()
>>> plt.tight_layout()

(Source code)